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Though December brought periods of unseasonable heat, the cold of winter is starting to grip the country. As humans, we have many methods of dealing with the chill. We bundle ourselves up in layers of wool from head to toe. We enjoy the warmth of fires, or perhaps just electric heaters. Our bodies are sure to let us know if we aren’t doing enough. Shivering contracts muscles swiftly and generates heat. Curling up minimizes surface area and prevents heat loss. However, one bodily reaction to the cold makes less sense: Goose bumps.

Courtesy of EverJean

The skin of a plucked goose has a bumpy appearance matching that of a cold human. Thus, the word "goose bumps" was born.

Goose bumps occur when tiny muscles at the base of hair follicles contract. This makes the hair rise, resulting in the classic puffed up and bumpy look. Cold isn’t the only cause of goose bumps. Fear can also provoke this response, as can other powerful emotions. Even positive feelings, if strong enough, can cause goose bumps to appear. Goose bumps seem to serve little purpose in modern humans, so why do we still experience them? For an explanation, we have to look back into our evolutionary history.

Human skin is rather unusual for a mammal. We have sparse hair covering our bodies while almost every other mammal has a coat of fur. By looking at ourselves, we can find evidence that human ancestors were once furred too. One of these clues is our goose bumps.

Courtesy of Joseph Dzikiewicz

Raised fur and an arched back are part of the posture of a frightened cat.

Goose bumps are a useful adaptation for many mammals. When a cat gets goose bumps its fur will stand on end. This provides insulation for a cold cat and makes a frightened cat appear larger to potential enemies. When humans get goose bumps, the body is “remembering” a time when this action functioned like it does in cats. We still get goose bumps even though our fur is long gone. It is an evolutionary relic that gives us no benefit now, but that helped our ancestors survive in a hostile world.

Next time you’re watching a scary movie and feel the goose bumps prickling your neck, remember where this response came from and imagine how different life would be if you fluffed up like a cat whenever you were startled!